As fall nights get cooler, heating systems start to operate… and the air in our homes becomes drier and drier. That’s because heating systems remove moisture from the air. The colder it is, the more you heat and drier the air becomes. The atmospheric humidity in the average home can fall to 13% on a cold winter’s day… that’s less than in the Sahara desert (25%)! Dry air is bad for our health, damages our paintings, causes wood furniture and wood flooring to crack… and is incredibly bad for our houseplants.
Most houseplants come from humid tropical environments. Air humidity can easily be 70% or above. Most will do all right at 60% and survive — but not thrive — at 50%. Below 50% and they are in trouble.
How to Tell If Dry Air is Harming your Plants?
The effects of dry air are not always easy to see, but you may notice them in the care you give your plants.
Logically, houseplants should require less watering in winter, since their growth has slowed down because of the decrease in sunlight. But if the air is very dry, they’ll be losing a lot of water to transpiration: every time they open their stomata to breathe (necessary in carrying out photosynthesis), they lose water. So one clear sign that the air is too dry is that you need to water as often in winter as during summer or even more frequently.
The plants that suffer the most visibly from dry air are those with thin leaves: brugmansias, abutilons, palms, ferns, etc. Often their leaves curl slightly down, their edges or tip dry out or blacken, they may hang limply even after you water or, most obvious of all, they simply fall off.
Plants with thick, leathery or waxy foliage are comparatively resistant to dry air, as are plants with very hairy leaves. They do suffer, but not as obviously as thin-leaved plants. Succulents — crassulas, sedum, cacti, etc. — are in this category, as are peperomias and rubber plants (Ficus elastica). They usually seem all right at first, but as the heating seasons drags on, you may start to see lower leaves drop off.
A secondary symptom is poor blooming. When the air is dry, flowers may abort before you even see them. If they do open, they often wilt or just don’t last as long as they should, even if the plant itself is relatively resistant to dry air. The thick, hairy leaves of the African violet, for example, are quite resistant to dry air, but the flowers suffer.
What to Do?
For the above reasons, it is always wise to increase humidity in the rooms where you grow houseplants.
The most obvious way is to run a humidifier or to grow them over a humidity tray. Or simply grow a lot of plants: since each plant gives off moisture during transpiration, the more plants you have, the greater the atmospheric humidity.
Lowering the thermostat at night temporarily increases ambient humidity and is also very effective. Or grow your plants in a room that is naturally more humid than the others, such as a laundry room or bathroom (assuming that there is some sunlight!).
To maintain high humidity at all times for the most sensitive plants, though, the ideal solution is to place them in a terrarium… or to seal them inside in a clear plastic bag. There they will remain in superb condition throughout the winter: humidity in a terrarium or a closed bag is as high as in a jungle and plants simply adore it!
One treatment that doesn’t work is spraying plants manually with water, typically with a recycled Windex bottle. Even if you often see this recommended, it’s a total waste of time. The effect only lasts a few minutes, plus it stains the leaves, not to mention the furniture. Try anything else but this!
So there you go: a few tips on how to keep your plants happy during the heating season: put them into practice and you’ll soon have a real jungle of thriving foliage in your home!